The invention relates to the structure and fabrication of electrical inductors and, in particular, to an inductor forming an integral part of an integrated circuit, such as a microprocessor, or forming an integral part of an integrated circuit package.
In the field of microelectronic circuits there is an incessant competitive pressure among manufacturers to drive the performance of their circuits up while driving down production costs. This is particularly true in the field of microprocessors, where each generation of devices is expected to provide greater performance than its predecessor, to operate at increasingly higher clock speeds and increasingly lower supply voltages, and to be fabricated as cheaply as possible.
Microprocessors currently being designed will require in excess of 100 watts of power to operate, and they will operate at supply voltages of about 1 volt, so the resulting current flowing through them will be nearly 100 amps.
At the same time that the speed and power requirements of commercially competitive microelectronic circuits are constantly increasing, there is an increasingly significant need to provide passive electrical devices such as inductors and transformers directly on such circuits or as part of the integrated circuit package. Due to the high operational current expected in these devices, it is important that they be relatively low in resistance in addition to being small in size and relatively inexpensive to fabricate.
Low resistance inductors and transformers are needed in numerous microelectronic applications, such as high frequency circuits, amplifiers, circuits for reducing electromagnetic interference (EMI), power converters (including direct-current to direct-current, alternating-current to alternating-current, direct-current to alternating current, and alternating-current to direct-current converters) for the distribution of power to circuits, and clocking circuits. In addition, other applications include radio frequency (RF) circuits such as are used in a myriad of wireless devices like cellular telephones, wireless modems, and other types of communications equipment.
Various integrated circuit inductors are known in the semiconductor art. For example, the following patents were found in the course of a search for art relating to the inventions described herein: U.S. Pat. Nos. 5,095,357, 5,635,892, 5,801,100, 5,877,533, all of which disclose various types of integrated circuit inductor structures. However, none of the known integrated circuit inductors are suitable for use in commercially competitive, high performance, low cost microcircuits, where the requirement is for low resistance, functionally effective, and relatively uncomplicated structures and processes. Some of the inductor structures disclosed in the above-mentioned patents are formed in a planar, spiral pattern, a disadvantage of which is that the magnetic flux goes down into the integrated circuit structure, causing the generation of mirror currents which can harm other circuit components.
For the reasons stated above, there is a substantial need in the semiconductor art for an inductive element for an integrated circuit and for an integrated circuit package, and method of fabrication thereof, which have relatively low resistance and which are relatively inexpensive to manufacture.
In addition, there is a substantial need in the semiconductor art for an integrated circuit and for an integrated circuit package having one or more inductive elements which have relatively low resistance and which are relatively inexpensive to manufacture.